Location of the Prime Meridian
The Prime Meridian is the meridian (line of longitude) that goes through the Royal Observatory, Greenwich in London it is also known as the International Meridian or Greenwich Meridian.
Gerardus Mercator in his Atlas Cosmographicae (1595) uses a prime meridian somewhere close to 25°W, passing just to the west of Santa Maria Island in the Atlantic. His 180th meridian runs along the Strait of Anián (Bering Strait)
Ptolemy's 1st projection, redrawn under Maximus Planudes around 1300, using a prime meridian east of Africa
Diogo Ribeiro's map of 1529, now in the Vatican library
1571 Africa map by Abraham Ortelius, Cabo Verde prime meridian
Markings of the prime meridian at the Royal Observatory, Greenwich.